That’s a nice set of bare earth points you have there…

The State of North Carolina ( where I reside)  has a lot of GIS data.  I am , in particular, intrigued by the statewide lidar data set.  Lidar , for the uninformed, stands for Light Detection And Ranging.  You basically find out how far away things are by shooting a laser pulse at them and measuring the amount of time it takes to hit the thing and bounce back.

This can be very useful if you mount your laser  in an airplane and shoot it at the ground.  You can then measure the distance between the plane and the ground.  If you know the exact location of the plane via GPS, then you know the elevation of the ground at that point.  Take points continuously as you fly the plane and you get a pretty good picture of what the ground surface looks like.  The ground surface can be mapped to within 6″-9″ in vertical accuracy.

Why does the state of North Carolina have statewide lidar data?  Well it’s because of Floyd. Not Floyd the barber from the
Andy Griffith Show

Floyd the Barber - not a hurricane .

I’m talking about Floyd the hurricane, a tropical cyclone that came ashore in North Carolina in 1999.
Hurricane Floyd
Floyd dropped a lot of rain (> 18 inches) on coastal North Carolina a few weeks after hurricane Dennis dropped 15 inches of rain on the same areas.  The floods that followed caused a lot of damage, and highlighted the  inaccuracy of  the existing paper floodplain maps.

In response,  the State of North Carolina set up the North Carolina Floodplain Mapping Program with the purpose of accurately mapping the floodplains.  The program chose lidar as the method of obtaining a land surface to model the hydrology of each watershed to determine the floodplain extent. Lidar data was collected for the entire state over the course of about 5 years 2001-2006. How much data is that? Quite a bit, but I’ll save that for my next post…

Continued soon

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Hello world! I like big data sets!

Greetings!  As a way of introduction, I’m a GIS professional ( GIS stands for Geographic Information Systems)  that has been working in the field for more than 20 years.  I have a strong interest in open source software in general (linux user since 1996) and open source GIS software  and thought I would start a blog on the subject of open source gis software and what you can do with it, at home.

I like working with large datasets and performing scripted ( mostly python ) operations to process vector and raster datasets.  So, with my bride’s consent, acquired a used server with a quad core CPU , boosted the RAM up to 16 GB , and added 2 x 2TB drives. ( I actually looked at  building a new workstation from scratch.  It would have cost around $1000.  This way was cheaper, even though the clock speed is slower)

I live in North Carolina, so I acquired the raw bare earth lidar data for North Carolina , and I’ve been playing with that dataset.    I’ll describe that process in my next post ( Hint: The dataset in the picture at the top of the blog was generated from the complete ASCII bare earth lidar dataset for the state of North Carolina, 8.5 billion points) .

Off to celebrate the New Year!



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